1. Field of the Invention
The present invention relates to a transfer system for use in a semiconductor wafer fab operating with both sealed SMIF pods and open lot carrier boxes, and in particular to a transport system for transferring workpiece carriers between SMIF pods and lot carrier boxes.
2. Description of Related Art
A typical semiconductor wafer fab includes a plurality of tool bays, each on the order of about eighty feet long, consisting in general of a number of processing tools for performing various wafer fabrication processes, and at least one stocker, where the wafers may be stored before and/or after processing. Various automated transport systems are further provided for transporting the wafers from one processing tool bay to another (interbay delivery systems), and for transporting the wafers around within each particular bay (intrabay delivery systems).
The wafers are transported around the fab within cassettes, which cassettes are themselves transported either bare or housed within enclosed containers. One type of conventional enclosed container is a so-called wafer lot carrier box (xe2x80x9clot boxxe2x80x9d) which encloses the wafers but does not seal the wafers off against the fab environment.
A second type of conventional container is a so-called standard mechanical interface (xe2x80x9cSMIFxe2x80x9d) pod which is sealed against the fab environment. A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system in general has three main components: (1) the sealed pods used for storing and transporting wafer cassettes; (2) a minienvironment supplied with ultraclean air flows surrounding cassette load ports and wafer processing areas of processing stations so that the environments inside the pods and minienvironment become miniature clean spaces; and (3) robotic input/output (I/O) transfer assemblies to transfer the wafer cassettes and/or wafers between the sealed pods and the processing equipment without contamination of the wafers in the wafer cassette from external environments.
The SMIF system is able to maintain the wafers in an ultraclean environment that is at least an order of magnitude cleaner than the environment of the surrounding wafer fab. Typical advanced semiconductor processes today employ geometries which are one-half micron (xcexcm) and under, and contamination particles having geometries of as little as 0.1 xcexcm can be very damaging to the processed semiconductor. As such, the SMIF solution is becoming widely used as a means for transporting semiconductor wafers around the wafer fab and between process tools in a substantially particle-free environment.
While SMIF technology provides significant advantages over conventional lot box transport, many fabs still have systems employing the latter. There is at present a need for an approach allowing a wafer fab to operate with both lot boxes and SMIF pods.
It is therefore an advantage of the present invention to provide a system allowing a wafer fab to operate with both lot boxes and SMIF pods.
It is a further advantage of the present invention to provide a mechanism capable of transporting workpiece carriers between lot boxes and SMIF pods.
It is another advantage of the present invention to provide a system where workpiece carriers may be positioned at the carrier transport mechanism by a stationary support platform mounted to the transport mechanism or by automated car which transports the carrier around the fab.
These and other advantages are provided by the present invention, which in preferred embodiments relates to a wafer transport mechanism capable of transferring workpiece cassettes between lot boxes and SMIF pods. The transport mechanism includes a frame having a first support platform on a first side of the frame for supporting a SMIF pod, and a second support platform on a second side of the frame for supporting a lot box. The frame further includes a carrier transfer mechanism which resides completely within the frame when in a home position. The transfer mechanism includes an arm and a gripper pivotally mounted to the arm.
A SMIF pod and lot box are initially loaded onto their respective platforms, and opened. Once the tops have been lifted, the gripper is positioned adjacent a cassette in the lot box, where it grips the handle on top of the cassette. The workpieces within the cassette are initially vertically oriented. The transfer mechanism lifts and rotates the cassette so that the workpieces are then oriented in a substantially horizontal plane. The transfer mechanism then sets the cassette down on the pod door seated on the first support platform. Thereafter, the pod top is lowered to once again mate with the pod door, and the latching mechanism within the pod door couples the top and door together so that the pod is sealed. The pod may thereafter be transferred away from the first support platform. The same process may be carried out in the reverse to transfer a workpiece cassette from the SMIF pod on the first support platform to the lot box on the second support platform.
In a preferred embodiment, the first and second support platforms are fixedly mounted to the frame. However, in an alternative embodiment, the support platform for supporting the SMIF pod and/or the lot box may be provided on an automated car for transporting the SMIF pod and/or lot box around the fab. When it is desired to drop off or acquire a wafer cassette, the car is positioned adjacent the frame, and cassette transfer is accomplished as described above.